Wavelength converting particle, method for manufacturing wavelength converting particle, and light emitting diode containing wavelength converting particle

ABSTRACT

Provided are a wavelength converting particle, a method for manufacturing a wavelength converting particle, and a light-emitting diode containing a wavelength converting particle. The wavelength converting particle comprises an organic/inorganic/hybrid perovskite nanocrystal that converts a wavelength of light generated by an excitation light source into a specified wavelength. Accordingly, it is possible to optically stabilize and improve color purity and light-emission performance without changes in a light-emitting wavelength range.

TECHNICAL FIELD

The present invention relates to a wavelength-converting particle, a method of manufacturing a wavelength converting particle, and a light-emitting diode (LED) containing a wavelength converting particle, and more particularly, to a wavelength converting nanoparticle containing organic/inorganic/hybrid perovskite nanocrystals, a method of manufacturing a wavelength-converting nanoparticle containing halide perovskite nanocrystals, and an LED containing a wavelength-converting nanoparticle containing a hybrid perovskite nanocrystals.

BACKGROUND ART

A light-emitting diode (LED) is a semiconductor device that converts electric current into light and is mainly used as a light source of a display device. Such an LED exhibits very excellent properties in terms of a small size, low power consumption, a long lifetime, and a fast response time when compared to conventional light sources. In addition, an LED is environment-friendly because it does not release harmful electromagnetic waves such as ultraviolet light and also does not use mercury and other discharge gases. An LED is usually formed by combining an LED light source using a wavelength converting particle such as a phosphor.

Conventionally, a colloidal quantum dot has been used as the wavelength converting particle. A quantum dot generates stronger light at a narrower spectral width than a typical phosphor. Light emission of a quantum dot is achieved when excited electrons transit from the conduction band to the valence band. The same material has a wavelength that varies depending on its size. A quantum dot may emit light of a shorter wavelength as the quantum dot decreases in size. Accordingly, it is possible to obtain light of a desired wavelength region by adjusting the size of the quantum dot.

A quantum dot may emit light even when an excitation wavelength is arbitrarily selected. Accordingly, it is possible to observe light of several different colors at once by exciting several kinds of quantum dots with a single wavelength excitation light. Also, since a light emission in a quantum dot only occurs through the transit from the conduction band minimum to the valence band maximum, a light emission generally has single emission color.

A quantum dot is a nanocrystal of a semiconductor material having a diameter of about 10 nm or less. A vapor deposition method such as metal organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE) or a chemical wet method in which precursors are inserted into an organic solvent to grow a crystal is used to form the quantum dot. The chemical wet method, which is a method of adjusting crystalline growth with an organic solvent naturally coordinated on a quantum dot determination surface to serve as a dispersing agent when a crystal is grown, has advantages over a vapor deposition method such as MOCVD or MBE because the chemical wet method can adjust uniformity in size and form of a colloidal nanocrystal through an easier and cheaper process.

However, a quantum dot has disadvantages in that the quantum dot is too unstable to be used as a wavelength converting material and has a limited color purity and luminescent effect. Accordingly, developing a wavelength converting material that is more stable and has improved color impurity and light emission performance is urgently required.

DETAILED DESCRIPTION OF THE INVENTION Technical Problem

The present invention is designed to solve the above problems and is directed to providing a wavelength converter that is optically stable and has enhanced color purity and light emission performance, a manufacturing method therefor, and a light-emitting diode (LED) containing the same.

Technical Solution

One aspect of the present invention provides a wavelength converting nanoparticle. The wavelength converting nanoparticle includes an organic/inorganic/hybrid perovskite hereafter, “perovskite” nanocrystal that converts a wavelength of light generated by an excitation light source into a specified wavelength.

The perovskite colloidal nanoparticles may include a perovskitemetal halide perovskite nanocrystals characterized by being capable of being dispersed in an organic solvent, may have a size ranging from 1 nm to 900 nm, and may have band gap energy ranging from leV to 5 eV.

The perovskite wavelength converting nanoparticle may further include a plurality of organic ligands that surround the perovskite halide perovskite nanocrystal. The organic ligands may include alkyl halides.

The perovskites may include a structure of A₂BX₄, ABX₄, ABX₃, or A_(n-1)B_(n)X_(3n+1) (n is an integer ranging from 2 to 6). Here, A may be organic ammonium or metal, B may be a metallic material, and X may be a halogen element. A may be (CH₃NH₃)_(n), ((C_(x)H_(2x+1))_(n)NH₃)₂(CH₃NH₃)_(n), (RNH₃)₂, (C_(n)H_(2n+1)NH₃)₂, (CF₃NH₃), (CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂(CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂, or (C_(n)F_(2n+1)NH₃)₂ (n is an integer greater than or equal to 1 and x is an integer greater than or equal to 1), B may be a divalent transition metal, a rare earth metal, an alkaline earth metal, Pb, Sn, Ge, Ga, In, Al, Sb, Bi, Po, or a combination thereof, and X may be Cl, Br, I, or a combination thereof.

Another aspect of the present invention provides a manufacturing method for a wavelength converting nanoparticle. The manufacturing method includes preparing a first solution, which has a perovskite precursor dissolved in a protic solvent, and a second solution, which has an alkyl halide surfactant dissolved in an aprotic solvent; and forming a nanoparticle by mixing the first solution with the second solution. Here, the wavelength converting nanoparticle includes a perovskite nanocrystal that converts a wavelength of light generated by an excitation light source into a specified wavelength.

The forming of a colloidal perovskitenanoparticle by mixing the first solution with the second solution may include adding the first solution to the second solution in drops. The perovskites may include a structure of A₂BX₄, ABX₄, ABX₃, or A_(n-1)B_(n)X_(3n+1) (n is an integer ranging from 2 to 6). Here, A may be organic ammonium or hybrid, B may be a metallic material, and X may be a halogen element. A may be ((CH₃NH₃)_(n), ((C_(x)H_(2x+1))_(n)NH₃)₂(CH₃NH₃)_(n), (RNH₃)₂, (C_(n)H_(2n+1)NH₃)₂, (CF₃NH₃), (CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂(CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂, or (C_(n)F_(2n+1)NH₃)₂ (n is an integer greater than or equal to 1 and x is an integer greater than or equal to 1), B may be a divalent transition metal, a rare earth metal, an alkaline earth metal, Pb, Sn, Ge, Ga, In, Al, Sb, Bi, Po, or a combination thereof, and X may be Cl, Br, I, or a combination thereof.

Another aspect of the present invention provides a perovskite wavelength converting layer. The wavelength converting layer includes the above-described wavelength converting nanoparticle.

Another aspect of the present invention provides a wavelength converter. The wavelength-converter includes the above-described wavelength converting nanoparticles; a dispersion medium configured to disperse the wavelength converting nanoparticle; and a sealing member configured to seal the wavelength converting nanoparticle and the dispersion medium, wherein the wavelength converting particle is dispersed in the dispersion medium. The dispersion medium may be in a liquid state initially.

Still another aspect of the present invention provides a light-emitting device. The light-emitting device includes a base structure; at least one excitation light source disposed on the base structure and configured to emit light of a predetermined wavelength; and a wavelength converting layer disposed along an optical path of the excitation light source and including the above-described wavelength converting nanoparticle. The wavelength converting layer may include a perovskite wavelength converter including the wavelength converting nanoparticle; a dispersion medium configured to disperse the wavelength converting nanoparticle; and a sealing member configured to seal the wavelength converting nanoparticle and the dispersion medium, wherein the wavelength converting particle is dispersed in the dispersion medium.

Advantageous Effects of the Invention

According to the present invention, it is possible to implement a wavelength conversion particle that is optically stable and has enhanced color purity and light emission performance without changes in a light-emitting wavelength band thereof due to a particle size because the wavelength converting particle contains an organic/inorganic/hybrid perovskite nanocrystal.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a wavelength converting nanoparticle containing a perovskite nanocrystal according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a manufacturing method for a wavelength converting nanoparticle containing a perovskite nanocrystal according to an embodiment of the present invention.

FIG. 3 is a schematic diagram of a perovskite nanocrystalline structure according to an embodiment of the present invention.

FIG. 4 is a schematic diagram showing a method of manufacturing a wavelength converting nanoparticle containing a perovskite nanocrystal through an inverse nano-emulsion method at various temperature according to an embodiment of the present invention.

FIG. 5 shows a wavelength converting layer according to an embodiment of the present invention.

FIGS. 6A to 6E are cross-sectional views illustrating a sealing method for a wavelength converter according to an embodiment of the present invention.

FIG. 7 is a cross-sectional view of a light-emitting diode (LED) according to an embodiment of the present invention.

FIG. 8 shows an LED according to another embodiment of the present invention.

FIG. 9 shows a fluorescent image obtained by photographing light that is emitted when ultraviolet light is emitted to a wavelength conversion material of a manufactured example and perovskite films according to Comparative Example 1 and Comparative Example 2.

FIG. 10 is a schematic diagram of wavelength-converting particles according to the manufactured example and Comparative Example 1.

FIG. 11 shows images obtained by photographing photoluminescence matrices of the wavelength converting particles according to the manufactured example and Comparative Example 1 at normal temperature and low temperature.

FIG. 12 shows a result graph obtained by photographing photoluminescence of the wavelength converting particles according to the manufactured example and Comparative Example 1.

MODE OF THE INVENTION

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings to describe the present invention. The present invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Like reference numerals refer to like elements throughout the specification.

<Wavelength Converting Particle>

A wavelength converting nanoparticle containing a perovskite nanocrystal that converts a wavelength of light generated by an excitation light source into a specified wavelength according to an embodiment of the present invention will be described below.

When light incident from the outside (incident light) reaches the above-described perovskite wavelength-converting particle, the wavelength converting particle emits light converted in wavelength. Accordingly, a wavelength converter functions to covert a wavelength of light through the perovskite wavelength-converting particle. Hereinafter, a portion of the incident light having a wavelength shorter than that of light emitted by the above-described perovskite wavelength-converting particle is referred to as excitation light. Also, a light source that emits the above-described excitation light is referred to as an excitation light source.

FIG. 1 is a schematic diagram showing a wavelength converting nanoparticle containing a perovskite nanocrystal according to an embodiment of the present invention.

Referring to FIG. 1, a wavelength converting particle according to an embodiment of the present invention, which is a perovskite nanoparticle, includes a perovskite nanocrystal 21 having a lamellar structure composed of alternating organic and inorganic planes.

The nanocrystal may have a band gap adjustable by halogen element substitution. The nanocrystal may have band gap energy ranging from 1 eV to 5 eV.

For example, the band gap may be adjusted by organic element substitution or center metal substitution.

Such a perovskite may include a structure of A₂BX₄, ABX₄, ABX₃, or A_(n-1)B_(n)X_(3n+1) (n is an integer ranging from 2 to 6). Here, A is an organic ammonium or inorganic material, B is a metallic material, and X is a halogen element. For example, A may be (CH₃NH₃)_(n), ((C_(x)H_(2x+1))_(n)NH₃)₂(CH₃NH₃)_(n), (RNH₃)₂, (C_(n)H_(2n+1)NH₃)₂, (CF₃NH₃), (CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂(CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂, or (C_(n)F_(2n+1)NH₃)₂ (n is an integer greater than or equal to 1 and x is an integer greater than or equal to 1). B may be a divalent transition metal, a rare earth metal, an alkaline earth metal, Pb, Sn, Ge, Ga, In, Al, Sb, Bi, Po, or a combination thereof. In this case, the divalent transition metal may be, for example, Ge, Sn, Pb, Eu, or Yb. Also, the alkaline earth metal may be, for example, Ca or Sr. Also, X may be Cl, Br, I, or a combination thereof.

A wavelength converting nanoparticle 20 containing a perovskite nanocrystal according to the present invention may additionally contain a plurality of organic ligands 22 surrounding the perovskite nanocrystal 21. In this case, the organic ligands 22, which are used as a surfactant, may include alkyl halides. Accordingly, the alkyl halides used as the surfactant to stabilize a surface of such a perovskite separated in the above-described manner become the organic ligands surrounding a surface of the perovskite nanocrystal.

When an alkyl halide surfactant has a shorter chain length, a nanocrystal formed therewith has a larger size and may have a size greater than 900 nm. In this case, there may be a fundamental problem in that excitons are separated as free charges and disappear, instead of being used to emit light, due to thermal ionization and charge carrier delocalization in a large nanocrystal.

That is, the size of the perovskite nanocrystal is inversely proportional to the length of the alkyl halide surfactant used to form the nanocrystal.

Accordingly, it is possible to adjust the size of the perovskite nanocrystal to a certain size or smaller by using alkyl halides of a certain size or larger as the surfactant. For example, a perovskite nanocrystal having a size ranging from 1 nm to 900 nm may be formed by using octadecyl ammonium bromide as the alkyl halide surfactant.

FIG. 2 is a flowchart showing a manufacturing method for a wavelength converting nanoparticle containing a perovskite nanocrystal according to an embodiment of the present invention.

Referring to FIG. 2, the manufacturing method for a wavelength converting nanoparticle containing a perovskite nanocrystal may include preparing a first solution having a perovskite dissolved in a protic solvent and a second solution having an alkyl halide surfactant dissolved in an aprotic solvent (S100) and forming a nanoparticle by mixing the first solution with the second solution (S200).

That is, the wavelength converting nanoparticle containing the perovskite nanocrystal according to an embodiment of the present invention may be manufactured through an inverse nano-emulsion method.

In detail, first, the first solution having the perovskite dissolved in the protic solvent and the second solution having the alkyl halide surfactant dissolved in the aprotic solvent are prepared (S100).

In this case, the protic solvent may include, but is not limited to, dimethylformamide, gamma butyrolactone, N-methylpyrrolidone, or dimethylsulfoxide.

Also, the perovskite may be a material having a crystalline structure. For example, the perovskite may have a structure of A₂BX₄, ABX₄, ABX₃, or A_(n-1)B_(n)X_(3n+1) (n is an integer ranging from 2 to 6).

Here, A is an organic ammonium material, B is a metallic material, and X is a halogen element.

For example, A cation may be (CH₃NH₃)_(n), ((C_(x)H_(2x+1))NH₃)₂(CH₃NH₃), (RNH₃)₂, (C_(n)H_(2n+1)NH₃)₂, (CF₃NH₃), (CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂(CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂, or (C_(n)F_(2n+1)NH₃)₂ (n is an integer greater than or equal to 1 and x is an integer greater than or equal to 1). Also, B may be a divalent transition metal, a rare earth metal, an alkaline earth metal, Pb, Sn, Ge, Ga, In, Al, Sb, Bi, Po, or a combination thereof. In this case, the divalent transition metal may be, for example, Ge, Sn, Pb, Eu, or Yb. Also, the alkaline earth metal may be, for example, Ca or Sr. Also, X anion may be Cl, Br, I, or a combination thereof.

FIG. 3 is a schematic diagram of a perovskite nanocrystalline structure according to an embodiment of the present invention.

Referring to FIG. 3, it can be seen that the perovskite nanocrystalline structure according to an embodiment of the present invention includes organic ammonium and halides.

Such a perovskite may be prepared by combining AX and BX₂ at a certain ratio. That is, the first solution may be formed by dissolving AX and BX₂ in a protic solvent at a certain ratio. For example, a first solution having an A₂BX₃ perovskite dissolved therein may be prepared by dissolving AX and BX₂ in the protic solvent at a ratio of 2:1.

Also, the aprotic solvent may include, but is not limited to, dichloromethane, trichlorethylene, chloroform, chlorobenzene, dichlorobenzene, styrene, dimethylformamide, dimethylsulfoxide, xylene, toluene, cyclohexene, or isopropyl alcohol.

Also, the alkyl halide surfactant may have a structure of alkyl-X. In this case, a halogen corresponding to X may include Cl, Br, or I. In this case, the structure of alkyl-X may include, but is not limited to, acyclic alkyl having a structure of C_(n)H_(2n+1), primary alcohol, secondary alcohol, and tertiary alcohol having a structure of C_(n)H_(2n+1)OH or the like, alkylamine having a structure of alkyl-N (e.g., hexadecyl amine or 9-Octadecenylamine 1-Amino-9-octadecene (C₁₉H₃₇N)), p-substituted aniline, phenyl ammonium, and fluorine ammonium.

Subsequently, a nanoparticle is formed by mixing the first solution with the second solution (S200).

The forming of a nanoparticle by mixing the first solution with the second solution preferably includes adding the first solution to the second solution in drops from a nozzle. In this reaction, the second solution may be agitated. For example, the nanoparticle may be synthesized by slowly adding the first solution having the perovskite dissolved therein to the second solution having the alkyl halide surfactant dissolved therein, which is being strongly agitated, in drops.

In this case, when the first solution is mixed with the second solution by drops, the perovskite is precipitated from the second solution because of a solubility difference therebetween. Also, the alkyl halide surfactant stabilizes a surface of the perovskite precipitated from the second solution to generate a well-dispersed organic/inorganic/hybrid perovskite nanocrystal. Accordingly, it is possible to manufacture a wavelength-converting nanoparticle film containing a hybrid perovskite nanocrystal that includes perovskite nanocrystals and a plurality of alkyl halide organic ligands surrounding the perovskite nanoscrystals.

Such a perovskite nanocrystal may be controlled in size by adjusting a length or shape factor of the alkyl halide surfactant. For example, the adjustment of the shape factor may be controlled through a tapered or an inversely triangular surfactant.

It is preferable that a perovskite nanocrystal generated in the above manner have a size ranging from 1 nm to 900 nm. When the perovskite nanocrystal is formed to have a size greater than 900 nm, there may be a fundamental problem in that excitons are separated as free charges and disappear, instead of being used to emit light, due to thermal ionization and charge carrier delocalization in a large nanocrystal.

FIG. 4 is a schematic diagram showing a method of manufacturing a wavelength converting nanoparticle containing a hybrid perovskite nanocrystal through an inverse nano-emulsion method according to an embodiment of the present invention.

Referring to FIG. 4A, the first solution having the perovskite dissolved in the protic solvent is added in drops to the second solution having the alkyl halide surfactant dissolved in the aprotic solvent.

In this case, the protic solvent may include, but is not limited to, dimethylformamide, gamma butyrolactone, N-methylpyrrolidone, or dimethylsulfoxide.

In this case, the perovskite may include a structure of A₂BX₄, ABX₄, ABX₃, or A_(n-1)B_(n)X_(3n+1) (n is an integer ranging from 2 to 6). Here, A is an organic ammonium material, B is a metallic material, and X is a halogen element. For example, A may be (CH₃NH₃)_(n), ((C_(x)H_(2x+1))_(n)NH₃)₂(CH₃NH₃)_(n), (RNH₃)₂, Cs, (C_(n)H_(2n+1)NH₃)₂, (CF₃NH₃), (CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂(CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂, or (C_(n)F_(2n+1)NH₃)₂ (n is an integer greater than or equal to 1). Also, B may be a divalent transition metal, a rare earth metal, an alkaline earth metal, Pb, Sn, Ge, Ga, In, Al, Sb, Bi, Po, or a combination thereof. In this case, the divalent transition metal may be, for example, Ge, Sn, Pb, Eu, or Yb. Also, the alkaline earth metal may be, for example, Ca or Sr. Also, X may be Cl, Br, I, or a combination thereof.

A structure of the perovskite may be formed by combining AX and BX₂ at a certain ratio. For example, a first solution having an A₂BX₃ perovskite dissolved therein may be prepared by dissolving AX and BX₂ in a protic solvent at a ratio of 2:1.

When A is CH₃NH₃ and X is Br as an example of a composition of AX, CH₃NH₃Br may be obtained by dissolving CH₃NH₂ (methylamine) and HBr (hydroiodic acid) in a nitrogen atmosphere and evaporating a solvent.

Referring to FIG. 4B, when the first solution is added to the second solution, the perovskite is precipitated from the second solution because of a solubility difference therebetween. An alkyl halide surfactant surrounds the perovskite and stabilizes a surface of the perovskite. Thus, the wavelength converting nanoparticle 20 containing a perovskite nanocrystal containing a well-dispersed hybrid perovskite nanocrystals is generated. In this case, the surface of the perovskite nanocrystal is surrounded by organic ligands, which are alkyl halides.

The wavelength converting nanoparticle containing the perovskite nanocrystal may be obtained by applying heat to selectively evaporate a protic solvent containing the wavelength converting nanoparticle 20 containing the perovskite nanocrystal, which is dispersed in an aprotic solvent having the alkyl halide surfactant dissolved therein, or by adding a co-solvent capable of being mixed with both of the protic solvent and the aprotic solvent to selectively extract the protic solvent containing the nanoparticle from the aprotic solvent.

The above-described wavelength converting nanoparticle may be dispersed in all organic solvents. Thus, the wavelength converting nanoparticle may be applied to various electronic devices because a size, a light-emitting wavelength spectrum, a ligand, and a constituent element thereof can be easily adjusted.

<Wavelength Converting Layer>

A wavelength converting layer including perovskite nanocrystals according to an embodiment of the present invention will be described below.

FIG. 5 shows a wavelength converting layer according to an embodiment of the present invention.

Referring to FIG. 5, the wavelength converting layer according to an embodiment of the present invention is a layer that includes the wavelength converting nanoparticle 20 containing a perovskite nanocrystal according to an embodiment of the present invention.

Since the wavelength converting particle has the same configuration and function as those described in the section <Wavelength converting particle>, reference will be made to the above description.

The above-described wavelength converting layer may be formed as a polymer resin in which wavelength converting particles 20 are uniformly dispersed. In this case, the polymer resin serves as a dispersion medium that disperses the wavelength converting particles 20. Any transparent medium that is not changed by light, does not reflect and absorb light, and does not affecting performance of the wavelength converting particle 20 may be used as the dispersion material.

As an example, it is preferable that the dispersion material be made of materials that have high light stability or moisture resistance and is not changed in color or quality by excitation light or the like, such as an epoxy resin or silicone.

The above-described dispersion medium may be in a liquid state. When the above-described dispersion medium is in the liquid state, the wavelength conversion particle 20 may be manufactured to be applied to various devices. Also, when the above-described dispersion medium is in the liquid state and the above-described wavelength conversion particle contains a plurality of organic ligands surrounding the perovskite nanocrystal, the wavelength converting particle may be applied to a device without separate ligand purification. Thus, it is possible to simplify a process thereof.

<Wavelength Converter>

A manufacturing method for a wavelength converter according to an embodiment of the present invention will be described below.

First, a wavelength converting particle is prepared.

Since the wavelength converting particle has the same configuration and function as those described in the section <Wavelength converting particle>, reference will be made to the above description.

Subsequently, the above-described wavelength converting particle is dispersed in a dispersion medium.

The wavelength converting particle is dispersed in the above-described dispersion medium. The dispersion medium may be initially in the liquid state. When the dispersion medium is in the liquid state and the dispersion medium and the wavelength converting particle dispersed in the dispersion medium are sealed by a sealing member, which will be described below, the dispersion medium and the wavelength converting particle are not limited by a shape of the sealing member and may be applied to various devices. For example, the dispersion medium may be an epoxy resin, or silicone rubber. It is preferable that the dispersion medium be made of a material that is not changed in color or quality by excitation light or the like because the wavelength converting particle receives excitation light and emits wavelength-converted light.

Subsequently, the wavelength converting particle and the dispersion medium are sealed with the sealing member.

FIGS. 6A to 6E are cross-sectional views illustrating a sealing method for a wavelength converter according to an embodiment of the present invention.

Referring to FIG. 6A, a first sealing member 10 a and a second sealing member 10 b are stacked.

A polymer or silicone resin that is not corroded by a dispersion medium 30 having the wavelength converting particle 20 dispersed therein may used as a sealing member. In particular, a polymer resin may be adhered to an object when it is heated, and thus a pack-type wavelength converter into which the dispersion medium 30 having the wavelength converting particle 20 dispersed therein is injected may be formed by adhering sheet-type polymer resin to the dispersion medium 30 through a thermal adherence process.

Referring to FIG. 6B, the first sealing member 10 a and the second sealing member 10 b may be adhered to each other through the thermal adherence process by heating the first sealing member 10 a and the second sealing member 10 b at one side 1 in order to prevent the above-described wavelength converting particle 20 and dispersion medium 30 from leaking through the sealing members 10 a and 10 b. However, an adherence process other than the thermal adherence process may be used when the above-described wavelength converting particle 20 and dispersion medium 30 do not leak.

Referring to FIG. 6C, the dispersion medium 30 having the wavelength converting particle 20 dispersed therein is injected between the first sealing member 10 a and the second sealing member 10 b at the other side at which the sealing members are not adhered to each other.

Referring to FIG. 6D, the dispersion medium 30 having the wavelength converting material 20 dispersed therein is sealed with the sealing members 10 a and 10 b by adhering the first sealing member 10 a and the second sealing member 10 b at the other side 1′ through the thermal adherence process.

Referring to FIG. 6E, it can be seen that a perovskite wavelength converter 400 in which the dispersion medium 30 having the wavelength converting material 20 dispersed therein is sealed with the sealing members 10 is formed. The above-described perovskite wavelength converter 400 may be advantageously applied to a light-emitting device without needing a separate ligand purification process by dispersing the wavelength converting nanoparticle 20 containing a perovskite nanocrystal, which is a wavelength converting material, in the dispersion medium 30 and sealing the wavelength converting nanoparticle 20 dispersed in the dispersion medium 30. Accordingly, it is possible to prevent oxidation of the wavelength converting particle due to ligand purification and thus exhibit a high color purity and luminescent performance when the perovskite wavelength converter 400 is applied to a light-emitting device. It is also possible to simplify a process thereof.

<Light-Emitting Device>

FIG. 7 is a cross-sectional view of a light-emitting device according to an embodiment of the present invention.

Referring to FIG. 7, a light-emitting device according to an embodiment of the present invention includes a base structure 100, at least one excitation light source 200 disposed on the base structure 100 and configured to emit light of a predetermined wavelength, and a wavelength converting layer 400B disposed along an optical path of the excitation light source 200 and containing the wavelength converting particle 20.

The base structure 100 may be a package frame or a base substrate. When the base structure 100 is a package frame, the package frame may include a base substrate. The base substrate may be a sub-mount substrate or a light-emitting diode (LED) wafer. The LED wafer indicates a state in which an LED element is formed on a wafer between, which is a state before the LED is separated in units of an LED chip. The base substrate may be a silicon substrate, a metal substrate, a ceramic substrate, or a polymer resin substrate.

The base structure 100 may be a packet lead frame or a package pre-mold frame. The base structure 100 may include bonding pads (not shown). The bonding pads may contain Au, Ag, Cr, Ni, Cu, Zn, Ti, Pd, or the like. External connection terminals (not shown) connected to the bonding pads may be disposed at an outer surface of the base structure 100. The bonding pads and the external connection terminals may be included in a package lead frame.

The excitation light source 200 is located on the base structure 100. It is preferable that the excitation light source 200 emit light of a wavelength shorter than a light-emitting wavelength of a wavelength converting particle of the wavelength converting layer 400B. The excitation light source 200 may be any one of an LED and a laser diode. Also, when the base structure 100 is an LED wafer, the positioning of the excitation light source may be omitted. For example, a blue LED may be used as the excitation light source 200, and a gallium nitride-based LED that emits blue light of a wavelength ranging from 420 nm to 480 nm may be used as the blue LED.

As shown in FIG. 8, a first encapsulation part 300 may be formed by pouring an encapsulation material for encapsulating the excitation light source 200 over the excitation light source 200. The first encapsulation part 300 may serve as a protective film and also serve to encapsulate the excitation light source 200. Also, when the wavelength converting layer 400B is located over the first encapsulation part 300, a second encapsulation part 500 may be additionally formed to protect and fix the wavelength converting layer 400B. The encapsulation material may include at least one of an epoxy, a silicone resin, acrylic polymers, a glass, carbonate polymers, and mixtures thereof.

The first encapsulation part 300 may be formed using various methods such as a compression molding method, a transfer molding method, a dotting method, a blade coating method, a screen coating method, a dip coating method, a spin coating method, a spray method, or an inkjet printing method. However, the first encapsulation part 300 may be omitted.

Since the wavelength converting layer 400B has the same configuration and function as those described in the sections <Wavelength converting layer> and <Wavelength converting particle>, reference will be made to the above description.

As shown in FIG. 7, the second encapsulation part 500 may be formed by pouring an encapsulation material for encapsulating the wavelength converting layer 400B over the wavelength converting layer 400B. The second encapsulation part 500 may be formed using the same material as the first encapsulation part 300 through the same method as the first encapsulation part 300.

The light-emitting device may be applied to a lighting unit, a backlight unit, or the like as well as a device for emitting light.

FIG. 8 shows an LED according to another embodiment of the present invention.

Referring to FIG. 8, the wavelength converting layer 400 may include a wavelength converter 400A, as shown in FIG. 6.

Since the wavelength converter 400A has the same configuration and function as those described in the sections <Wavelength converter> and <Wavelength converting particle>, reference will be made to the above description.

According to an embodiment of the present invention, the limit-emitting device has been shown as a unit cell. However, when the base structure is a sub-mount substrate or a LED wafer, multiple LED chips, each having a wavelength converting layer formed therein, may be located on the sub-mount substrate and the LED wafer, and the sub-mount substrate or the LED wafer may be cut and processed in units of a unit cell.

For a better understanding of the present invention, a preferred experimental example will be described below. However, the following experimental example is merely intended to facilitate an understanding of the present invention, and thus the present invention is not limited thereto.

Manufactured Example—Manufacture of Wavelength Converting Particle

A wavelength converting nanoparticle containing a perovskite nanocrystal according to an embodiment of the present invention was formed. The wavelength converting nanoparticle was formed through an inverse nano-emulsion method.

In detail, a first solution was prepared by dissolving a perovskite in a protic solvent. In this case, dimethylformamide was used as the protic solvent, and (CH₃NH₃)₂PbBr₄ was used as the perovskite. In this case, (CH₃NH₃)₂PbBr₄ was formed by mixing CH₃NH₃Br and PbBr₂ at a ratio of 2:1.

Subsequently, a second solution having an alkyl halide surfactant dissolved in an aprotic solvent was prepared. In this case, toluene was used as the aprotic solvent, and octadecylammonium bromide (CH₃(CH₂)₁₇NH₃Br) was used as the alkyl halide surfactant.

Subsequently, a wavelength converting particle containing a perovskite nanocrystal was formed by slowly adding the first solution to the second solution, which is being strongly agitated, in drops.

Comparative Example 1

A thin-film type perovskite (a perovskite film) was manufactured.

In detail, a thin film of (CH₃NH₃)₂PbBr₄ was manufactured by dissolving (CH₃NH₃)₂PbBr₄ in dimethylformamide, which was a protic solvent, to manufacture a first solution and then performing spin-coating on a glass substrate with the first solution.

Comparative Example 2

A thin-film type perovskite (a perovskite film) was manufactured.

In detail, a thin film of (CH₃NH₃)₂PbCl₄ was manufactured by dissolving (CH₃NH₃)₂PbCl₄ in dimethylformamide, which was a protic solvent, to manufacture a first solution and then performing spin-coating on a glass substrate with the first solution.

Experimental Example

FIG. 9 shows a fluorescent image obtained by photographing light that is emitted when ultraviolet light is emitted to a wavelength converting material of the manufactured example and perovskite films according to Comparative Example 1 and Comparative Example 2.

Referring to FIG. 9, it can be seen that the wavelength converting particle having the form of a nanoparticle according to the manufactured example emits very bright green light while the perovskites having the form of a thin film other than a nanoparticle emit dim light.

Also, it can be seen, as a result of measuring a photoluminescence quantum yield (PLQY), that the perovskite particle according to the manufactured example exhibit very high values.

Conversely, the thin-film type perovskites according to Comparative Example 1 and Comparative Example 2 exhibit low PLQY values of about 1%.

FIG. 10 is a schematic diagram of wavelength converting particles according to the manufactured example and Comparative Example 1.

FIG. 10A is a schematic diagram of the wavelength converting particles according to Comparative Example 1, and FIG. 10B is a schematic diagram of the wavelength converting particles according to the manufactured example. Referring to FIG. 10A, the wavelength converting particles according to Comparative Example 1 are in the form of a thin-film. Referring to FIG. 10B, the wavelength converting particles according to the manufactured example are in the form of a nanoparticle 21.

FIG. 11 shows images obtained by photographing photoluminescence matrices of wavelength converting particles according to the manufactured example and Comparative Example 1 at normal temperature and low temperature.

FIG. 11A shows the image obtained by photographing the photoluminescence matrix of the thin-film type perovskite (perovskite film) according to Comparative Example 1 at low temperature (70K), and FIG. 11B shows the image obtained by photographing the photoluminescence matrix of the thin-film type perovskite (perovskite film) according to Comparative Example 1 at room temperature.

FIG. 11C shows the image obtained by photographing the photoluminescence matrix of the wavelength converting nanoparticle containing the perovskite nanocrystal according to the manufactured example at low temperature (70K), and FIG. 11D shows the image obtained by photographing the photoluminescence matrix of the wavelength converting nanoparticle containing the perovskite nanocrystal according to the manufactured example at room temperature.

Referring to FIGS. 11A to 11D, it can be seen that the wavelength converting nanoparticle containing the perovskite nanocrystal according to the manufactured example exhibits higher color purity than the thin-film type perovskite (perovskite film) according to Comparative Example 1 while exhibiting photoluminescence at the same position thereas. It can be also seen that the perovskite nanocrystal film according to the manufactured example exhibits photoluminescence with the same level of color purity at room temperature and low temperature and also does not decrease in luminescence intensity. Conversely, the thin-film type perovskite according to Comparative Example 1 has different color purity levels and luminescence positions at room temperature and low temperature and also exhibits low luminescence intensity at room temperature because excitons thereof are separated as free charges and disappear, instead of being used to emit light, due to thermal ionization and charge carrier delocalization.

FIG. 12 shows a result graph obtained by photographing photoluminescence of the wavelength conversion particles according to the manufactured example and Comparative Example 1.

Referring to FIG. 12, it can be seen that, when the perovskite nanoparticle according to the manufactured example is located in a solution, that is, in the liquid state, the perovskite nanoparticle exhibits higher color purity than the conventional perovskite according to Comparative Example 1 while exhibiting photoluminescence at the same peak wavelength position thereas.

The wavelength converting particle containing the nanocrystal including the perovskite according to the present invention may have a perovskite nanocrystal having a crystalline structure obtained by combining FCC and BCC formed therein, have a lamellar or layered structure composed of alternating organic and inorganic planes, and exhibit a high color purity because excitons are bound to the inorganic plane.

In a nanocrystal having a size ranging from 10 nm to 300 nm, an exciton diffusion length may decrease and also exciton binding energy may increase. Thus, it is possible to prevent quenching of excitons due to thermal ionization and charge carrier delocalization such that luminescent efficiency at room temperature is high.

Furthermore, by synthesizing a perovskite nanocrystal unlike the perovskite bulk crystals having a three-dimensional structure, it is possible to increase exciton binding energy to enhance luminescent efficiency while increasing durability and stability.

Also, according to the manufacturing method for a wavelength converting particle containing a perovskite nanocrystal according to the present invention, it is possible to synthesize a wavelength converting nanoparticle containing a perovskite nanocrystal adjusted in size depending on a length and size of an alkyl halide surfactant.

While the present invention has been particularly shown and described with reference to preferred embodiments thereof, the present invention is not limited to the embodiments, and various modifications and changes may be made therein by those skilled in the art without departing from the sprit and scope of the present invention.

DESCRIPTION OF REFERENCE NUMERALS

-   -   1: one side of sealing member     -   1′: other side of sealing member     -   10: sealing member     -   20: wavelength converting particle     -   30: dispersion medium     -   100: base structure     -   200: excitation light source     -   300: first sealing part     -   400B: wavelength converting layer     -   400A: wavelength converting body     -   500: second sealing part 

The invention claimed is:
 1. A wavelength-converting particle comprising: one or more nanocrystals of a perovskite having a nanocrystal size greater than 10 nm and smaller than 300 nm that is configured to absorb light having a first wavelength and emit light having a second wavelength, wherein the second wavelength of the light emitted from the perovskite does not change substantially over the nanocrystal size thereof unlike a quantum dot that substantially changes a wavelength of light emitted therefrom over a nanocrystal size thereof; and a plurality of ligands attached to the one or more nanocrystals and configured to make the one or more nanocrystals more dispersible than without such ligands in a medium.
 2. The particle of claim 1, wherein the one or more nanocrystals of the perovskite having a nanocrystal size greater than 10 nm and smaller than 300 nm have a band gap ranging from 1 eV to 5 eV.
 3. The particle of claim 1, wherein the plurality of ligands attached to the one or more nanocrystals surround the one or more nanocrystals.
 4. The particle of claim 3, wherein the ligands comprises alkyl halides.
 5. The particle of claim 1, wherein the perovskite has a crystal structure of A₂BX₄, ABX₄, ABX₃, or A_(n-1)B_(n)X_(3n+1) (n is an integer ranging from 2 to 6); and wherein A is organic ammonium or cation, B is a metal, and X is a halogen.
 6. The particle of claim 5, wherein: wherein A is (CH₃NH₃)_(n), ((C_(x)H_(2x+1))nNH₃)₂(CH₃NH₃)_(n), (RNH3)2, (C_(n)H_(2n+1)NH₃)₂, (CF₃NH₃), (CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂(CF₃NH₃)_(n), ((C_(x)F_(2x+1))_(n)NH₃)₂, metal, or (C_(n)F_(2n+1)NH₃)₂, wherein “n” is an integer greater than or equal to 1, and “x” is an integer greater than or equal to 1; wherein B is a divalent transition metal, a rare earth metal, an alkaline earth metal, Pb, Sn, Ge, Ga, In, Al, Sb, Bi, Po, or a combination thereof; and wherein X is Cl, Br, I, or a combination thereof. 